In the book "The Ceramic Spectrum" by Robin Hopper, he states that
copper can produce a purple and plum color in both oxidation and
reduction, cone 6 thru 10 in high alkaline or barium/zinc glazes. I
was wondering if anyone out there is familiar with this coloring from
copper. Anyone have a recipe? I would like to run some tests on this
type of glaze. If I had a proven recipe as a starting point, I could
probably save countless tests narrowing in on a workable glaze.
Also, I wonder if strontium could replace the barium and still retain
the coloring. Any hints? Thanks. - Mike
Oh, I generally fire to cone 6 oxidation, electric. I have been known
to fire higher if necessary. - Mike
i've used laguna clay's "turquoise matt" for cone 10 reduction fires.
it contains some of what you mention. i don't know the details, but
when i have pieces slightly underfired they take on more purple.
fast cooling also seems to freeze reds in place that otherwise seem to
settle out into less of a red in slower cooling kilns.
i used to have a kiln that could hit cone 10 in 4 hours, and cool off
in 1 1/2 hours. (i could do two cone 10 fires in a day). i used to
deliberately place redish glazed pieces next to this glaze and seemed
to get vapour deposits from one glaze over to this turquoise glaze.
possibly laguna clay can shed light on how the glaze is formed.
Most copper glazes will produce 'plumy' reds in reduction but I think
similar colours in oxidation would make use of cadmium.